First, a conventional induction heating cooker will be described. FIG. 3 is a view showing a configuration of conventional induction heating cooker 100.
As shown in FIG. 3, induction heating cooker 100 includes top plate 32 for holding pan 31, and heating coil 33 for heating pan 31 on a lower side of top plate 32.
Infrared sensor 35 is arranged at a central portion of heating coil 33, temperature calculating unit 37 calculates the temperature of a bottom of the pan according to an output from infrared sensor 35, and control unit 38 controls an output of inverter circuit 34 connected to heating coil 33 based on the temperature calculated in temperature calculating unit 37.
Waveguide 36 made of non-magnetic metal material such as aluminum for guiding infrared light radiated from pan 31 to infrared sensor 35 is arranged on an upper side of infrared sensor 35.
Furthermore, to reduce self-heating of waveguide 36 by the magnetic flux from heating coil 33, first magnetism prevention unit 39 of plate shape made from a material having high permeability such as ferrite is arranged below heating coil 33, and second magnetism prevention unit 40 of plate shape having high permeability such as ferrite is arranged on an inner side of heating coil 33 at the periphery of waveguide 36.
According to such configuration, infrared sensor 35 is prevented from being influenced by infrared light radiated from other than the bottom of pan 31, that is, waveguide 36 heated by the magnetic field generated by heating coil 33 in induction heating cooker 100 (see e.g., patent document 1).
However, in the conventional configuration described above, if pan 31 is heated in an empty pan state, the temperature might rapidly rise at the central portion (region B in FIG. 3) in the width direction of heating coil 33 where the magnetic flux density is the highest. In such case, even if the temperature of the bottom of the pan is detected with infrared sensor 35 arranged at the central portion (region A in FIG. 3) of pan 31 and controlled to lower than an ignition temperature of oil, the temperature of the bottom of the pan at the central portion in the width direction of heating coil 33 has a possibility of reaching a level of ignition temperature of the oil.
If the heating output is controlled with such method of detecting the bottom of the pan, in particular, if a thin stainless pan with poor heat conduction and low heat capacity is used, the bottom of the pan may be heated to red heat and the pan may be deformed if heated in an empty pan state.
The temperature of the portion of pan 31 that becomes a temperature higher than the upper part of the center of heating coil 33 can be detected by arranging infrared sensor 35 at the central portion in the width direction of heating coil 33 or arranging the same close to an inner periphery of a winding part at a central opening of heating coil 33. However, if infrared sensor 35, waveguide 36, and second magnetism prevention unit 40 are arranged at an intermediate portion of the winding parts of heating coil 33, the occupying space of such component becomes large. Therefore, it becomes difficult to mount close to the portion that becomes a higher temperature of pan 31 while reducing the influence on the shape of heating coil 33. If second magnetism prevention unit 40 is omitted to reduce the occupying space of the components such as infrared sensor 35, waveguide 36 may generate heat, and the temperature detection precision by infrared sensor 35 may lower from the influence of infrared light radiation of waveguide 36, as described above.
[Patent document 1] Unexamined Japanese Patent Publication No. 2005-38660